Studies on adsorption mechanism and kinetics of magnesium in selected cocoa growing soils in Nigeria

Several soil evaluations have found magnesium defic ient in most cocoa plantations in Nigeria. Authors have recommended the use of magnesium fertilizers to add ress the deficiency. For appropriate fertilizer app lication and effective utilization of applied fertilizer, understanding the adsorption kinetics and magnesium holdi ng capacity of each soil will help in making precise recommendatio n in order to prevent wasting of resources and cont amination of the environment with un-adsorbed magnesium. Soil sa mples were collected with soil auger at a depth of 0-30cm from selected cocoa plantations in Lodu, Itu, Ikom, Asaba and Uhonmora in Abia, Akwa Ibom, Cross River , Delta and Edo States respectively. One gram (1.0 g) of ea ch sample was equilibrated with 30ml of 20, 40, 60, 80 and 100 mg Mg L -1 solution. Another portion (1.0 g) of each sample w as equilibrated with 30ml of 70 mg Mg L -1 for 40, 80, 120 and 140 minutes to study the kinetics of Mg 2+ ions in soil. The data generated were fitted into various adsorption Isotherms and kinetic models. Results sh owed that, Freundlich model best described the adso rption of magnesium indicating Mg adsorption on heterogeneous surfaces. Mass transfer kinetic model best describ ed the kinetics of Mg 2+ adsorption. Sample obtained from Cross River State had the highest adsorption capacity for magnesium compared with the rest of the soils. Clay and organic carbon were the main soil properties t hat influenced Mg 2+ adsorption in the soils.